This invention relates generally to contact assemblies for small semiconductor devices and, more particularly, to a contact assembly for receiving, positioning, supporting, and contacting the semiconductor device without requiring separate die bonding and wire bonding steps.
Techniques for mounting, contacting and encapsulating small semiconductor devices such as diodes, transistors, thyristors, etc. are well known. In the past, such techniques have required wire bonding the contact regions of the device to a lead frame. Gold or aluminum wires are secured to the metalized surfaces of the device under compression and heat. These wires are generally very small in diameter (typically 0.5 mil-20 mil) and therefore, the equipment necessary to accomplish the bond is generally complex and expensive. Furthermore, due to the intricacy of the process, a great deal of time is required to reach the end result.
To overcome these problems, contact assemblies have been developed which inherently support the semiconductor device and at the same time resiliently engage the contact regions of the device such that the bonding of the device to the support and the joining of contacts to the metalized contact regions on the device may be accomplished in a single reflow step. Such a technique is taught in U.S. Pat. No. 3,500,136 entitled "CONTACT STRUCTURE FOR SMALL AREA CONTACT DEVICES" issued on Mar. 10, 1970. This patent describes an elongated contact spring which may be presented in a ladder lead frame format, wherein each spring is transversly segmented into a plurality of parallel segments. That is, each contact assembly consists of three separate segments which are deflectable with respect to each other. A semiconductor device is placed on the center segment and deflected with respect to the side segments such that internally projecting tangs from the sides of the outer two segments are pressed into engagement with electrodes on the upper surface of the semiconductor device. The lead frame assembly including a plurality of individual contact assemblies is then placed in a furnace and the semiconductor dies are soldered to their respective contacts. The semiconductor device portion may then be encapsulated and the groups of three segments for each device separated from segments associated with other devices.
Unfortunately, the apparatus described in the above referred to U.S. patent suffers several disadvantages. First, the tangs which form parts of the side segments of each contact assembly are stamped out of that portion of the center segment upon which the semiconductor device rests. Therefore, the semiconductor device is not entirely supported from beneath. The regions of nonsupport correspond to the regions of maximum pressure on the device since these regions correspond to the tangs engaging the upper surface of the semiconductor device. Additionally, the heat sinking capability of the center segment is substantially reduced.
One apparatus which partially solves the above problem is shown and described in U.S. Pat. No. 3,569,797 issued Mar. 9, 1971 and entitled "Semiconductor Device with Preassembled Mounting". In this device, the leads are formed to provide spring contact with an active element and also serve as an inserting and positioning fixture. The disclosed stamped lead frame includes a tab from which emitter, collector and base leads extend. The collector lead terminates in a rectangular mounting platform. The emitter and base leads terminate in backward and inward extending contact sections which provide spring pressure on the platform. A semiconductor device is then placed on the platform by deflecting either the platform or the emitter and base leads and then allowing the contact sections to come to rest on the device.
The above described device suffers certain disadvantages. First, the deflection of the leads in order to insert a semiconductor device on the platform may damage the leads. Second, it is difficult to position the semiconductor device on the platform for proper contact.
It is known, for example, to provide a pocket or seat on a base or substrate in order to properly position a semiconductor device for contact by a four-sided pocket for this purpose is shown in U.S. Pat. No. 4,346,396 issued Aug. 24, 1982 entitled "Electronic Device Assembly and Methods of Making Same". However, the use of such a pocket in the device of the apparatus of U.S. Pat. No. 3,569,797 would still require significant deflection of the leads. In addition to the above referred to disadvantages, there is no means for properly positioning the semiconductor device on the center segment to assure that the contact tangs of the side segments accurately engage the metalized contact regions. Therefore, additional time and effort must be consumed in order to achieve proper positioning prior to commencing the solder reflow step.